Chapter 12 - Solids and Modern Materials

Classifying solids based on bonds

• Metallic solids - Held together by a sea of collectively shared electrons.
• Ionic solids - Sets of cations and anions mutually attracted to one another.
• Covalent-network solids - Joined by an extensive network of covalent bonds.
• Molecular solids - Discrete molecules held together by weak forces.

Types of solids

• Polymers - Contain a long chain of atoms connected by covalent bonds. They have different properties than small molecules or metallic ionic compounds.
• Nanomaterials - Crystalline compounds with the crystals on the order of 1-100nm. They have different properties than larger crystalline materials.
• Crystalline - Solids with a repeating pattern of atoms.
• Amorphous - Lack of order in the arranged atoms.

Unit Cell

• Unit cell - The basis of a repeating pattern.
• The structure of a crystalline solid is defined by
  • Size and shape of unit cell
  • Location of atoms in the unit cell
• Crystal lattice - Geometric pattern on which the unit cell is.
• Lattice points - Positions that define the overall structure of the crystalline compound.
  • Each point has an identical environment.

Basic 3D lattices

• Cubic
• Tetragonal
• Orthorhombic
• Rhombohedral
• Hexagonal
• Monoclinic
• Triclinic

• Centered lattices - Have atoms in another regular location, most common in the body center (body-centered) or center of the face (face-centered).
• Alloys - Materials that contain more than one element and have the characteristic properties of metals.
  • Substitutional alloys - A second element takes the place of a metal atom.
  • Interstitial alloys - A second element fills a space in the lattice of metal atoms.
  • Heterogeneous alloys - Components are not dispersed uniformly.

Metallic bonding

• Electron sea model - Where we assume a metal is a group of cations suspended in a sea of electrons.
• Molecular solids - Consist of atoms of molecules held together by weaker forces.
  • Shape - Ability to stack, it has influence on some physical properties like boiling point.
• Covalent-network solids - Atoms are covalently bonded over large network distances with regular patterns of atoms.
  • They have higher melting and boiling points.
• Coordination number - The number of nearest-neighbor atoms of an atom.

Polymers

• Polymers - Molecules of high molecular weight made by joining smaller molecules called monomers.
  • They are mostly carbon-based.
  • They are formed by covalent bonding.

Primary polymers

• Addition - Formed when a bond breaks and the electrons in that bond make two new bonds.
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• Condensation - Formed when a small molecule is removed between two larger molecules.
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• Copolymers - Formed by two different monomers.

Semiconductors on nanometers

• Quantum dots - Semiconductor particles that are about 1-10nm.
• Bond energy - Gap between highest occupied level and lowest unoccupied level.
• Buckminsterfullerene or Buckyballs - Soccer ball-shaped C60 molecule.